<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>父级比例</title>
    <style>
        html {
            height: 100%;
        }
        
        body {
            height: 100%;
        }
        
        .box {
            background-color: pink;
            /* % 是相对于父级的百分比 */
            width: 50%;
            height: 50%;
        }
    </style>
</head>

<body>
    <div class="box">盒子</div>
</body>

</html>